The conventional structure of temperature control devices for maintaining an object to be controlled, such as an arrayed waveguide grating optical wavelength multiplexing/demultiplexing element at a preset constant temperature are generally composed of a soaking part 1 and a control part 6 as shown in FIG. 4 and FIG. 5.
The soaking part 1 includes a soaking plate 2 which is made from a good heat conductive material, a heater 40 which is embedded in the soaking plate 2, an object 10 to be controlled which is fixed on the soaking plate 2, and a temperature sensor 5 which is also fixed on the soaking plate 2 in such a manner as to be adjacent to the object 10 to be controlled.
The control part 6 makes a present temperature signal s2 which has been outputted from a temperature detection circuit 7 in accordance with a temperature detection signal s4 which has been transmitted from the temperature sensor 5 be compared with a target temperature signal s1 which has been outputted from a temperature setting circuit 8 that presets a heating target temperature by a comparator 9 or a control terminal circuit of a semiconductor control element 30 connected in series with the heater 40. Then, an error signal s3 which indicates the comparison result of the comparator 9 is inputted as a control signal to the control terminal of the semiconductor control element 30.
Thus, the conventional structure is based on a negative feedback control where the heater 40 is the only heat source, the temperature information from the temperature sensor 5 that is thermally coupled to the heater 40 is processed in the control part 6, and the current to be supplied to the heater 40 is controlled by the semiconductor control element 30 of the control part 6, thereby driving the heater 40 and maintaining the soaking plate 2 and the object 10 to be controlled at a constant temperature (See the description of the prior art in Japanese Unexamined Patent Application No. 9-306638, for example).
However, in the aforementioned prior art device, the semiconductor control element 30, which directly controls the current to be supplied to the heater 40, inevitably generates a high junction temperature. The heat generation demands that the semiconductor control element 30 includes a component for efficiently radiating its junction temperature. This causes the problem of making the structure of the control part 6 of the temperature control device complex, and as another problem the miniaturization of the arrayed waveguide grating optical wavelength multiplexer/demultiplexer using this temperature control device is substantially limited.
As a further additional problem, part of the electric power from the power supply to drive the heater 40 is wasted as the junction temperature of the semiconductor control element 30 and this loss in the semiconductor control element 30 becomes ineffective, thereby deteriorating the efficiency of the overall temperature control device.
The heat resistance value (temperature rise per 1 W) of the semiconductor control element 30 corresponds to the junction temperature, the case temperature of the arrayed waveguide grating optical wavelength multiplexer/demultiplexer and the atmospheric temperature. Between the case temperature and the atmospheric temperature, the heat resistance value corresponds to a heat sink (radiating means). As a further additional problem, the heat resistance value will be raised by the miniaturization of the temperature control device, whereby it becomes impossible to further improve the reliability of the temperature control device.
The present invention, which has been contrived to solve the aforementioned problems in the prior art device, has the technical challenge of eliminating the adverse effect of the junction temperature of the semiconductor control element in a temperature control device which maintains an object to be controlled at a preset constant temperature and in an arrayed waveguide grating optical wavelength multiplexer/demultiplexer using this temperature control device. And the present invention has the object of simplifying the structure of each of the temperature control device and the arrayed waveguide grating optical wavelength multiplexer/demultiplexer, and of improving operation efficiency sufficiently without any trouble.